1. Field of the Invention
The present invention relates to a highly conductive ink composition, and more particularly relates to a viscosity controllable ink composition with high conductivity.
2. Description of the Related Art
Advances in semiconductor manufacturing processes for integrated circuits or liquid crystal displays continuously reduce the size of the semiconductor device and increases the density of the circuits in order to obtain better efficiency. To meet these requirements, metal conductive patterns serving as a conductive lines or electrodes require greater integration density and shorter line widths.
In general, metal conductive patterns are formed on a substrate by a photolithography process, wherein the photolithography process comprises the following procedures: a metal layer is firstly formed on the substrate by chemical vapor deposition, plasma deposition, or spin coating; a photoresist layer is then coated on the metal layer; thereafter, the photoresist layer is then selectively exposed by a mask and UV-radiation; the exposed photoresist layer is then developed by a developing agent to form a patterned photoresist layer; finally, the metal layer is etched utilizing the patterned photoresist layer as an etching mask, so as to form a metal conductive pattern on the substrate.
Due to the great number of complicated steps in the photolithography process and the amount highly pure chemicals, expensive photoresist composition, and etching agents required, process costs are high and environmental protection suffers. Besides, many steps of the photo lithography process are requested to process in high temperature and/or high pressure environment. Thus, the process costs also get increasing. Moreover, metal vapor may diffuse in the manufacturing equipment under the high temperature environment when depositing metal layer, so as to degrade efficiency of electronic equipment and cause damage on equipment.
In order to solve the problem generated from forming a metal conductive pattern so far, so-called screen printing is further proposed to form a metal conductive pattern. Compared with photo lithography process, screen printing has more simple manufacturing procedure and process environment with relatively lower temperature. However, the formed patterned metal layer by screen printing has worse adhesion to the substrate, thus, peeling is easily occurred and yield decreases.
Compared with screen printing, conductive lines or electrode patterns fabricated by ink jet printing has benefits of computers in control and highly automation, so as to lower the manufacturing cost. In IEEE Transactions components Hybrids and Manufacturing Technology (Vol. 12(4), 1987, Pages 545-549), “Liquid ink-jet printing with MOD inks for hybrid microcircuits” published by R. W. Vest et al provides a method of forming a metal conductive pattern by ink-jet printing process, which utilizes a ink composition containing a metallo-organic decomposition compounds, MOD, decomposable at a low temperature followed by transferring to metal or metal oxide after forming a conductive pattern. Nevertheless, due to the viscosity of MOD solution is pretty low (<2 cP), the metal conductive layer produced by the ink composition is very thin, and the sheet resistance easily gets extremely high. Therefore, to reduce resistance, the ink jet printing process needs be reproduced multiple times to increase the total thickness by adding the formed metal conductive layers. Thus, the required time for process is prolonged, the process gets complicated, cost increases, and the short of the device is occurred resulted from the misalignment of the subsequently formed metal conductive layer makes.
Thus, a simpler manufacturing method for developing a metal conductive pattern, capable of improving the integrated circuit and liquid crystal display performance is desirable.